1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to an apparatus for adjusting pressure of a fixing unit, and an image forming apparatus having the same.
2. Description of the Related Art
An image forming apparatus generally operates to form a toner image onto a photosensitive medium, and transfer the toner image onto a printing medium. The image forming apparatus includes a fixing unit to fix the toner image onto the printing medium by heat and pressure.
The fixing (i.e., fusing) unit generally includes a heating roller to generate a high temperature heat, and a pressing roller to press against the heating roller with a predetermined pressing force. An elastic member is employed to support the pressing roller, such that the pressing roller presses the heating roller with a predetermined pressure. Accordingly, a toner image is fixed onto a printing medium when the printing medium passes between the heating roller and the pressing roller.
Because the fixing unit is usually set to have a specific pressing force, that is, set for standard printing paper, problems occur when a printing medium other than standard printing paper is passed through the fixing unit. For example, if an envelope, which is thicker than standard printing paper, is passed through the heating and pressing rollers, the envelope will usually have a crease.
In order to solve the above problem, an image forming apparatus is conventionally provided with a separate manually-operable lever, to adjust the pressure exerted on the pressing roller by the elastic member in accordance with the thickness of the printing medium. That is, in order to print on an envelope, a user operates the manually-operable lever to adjust the pressing force of the pressing roller and to prevent generation of a crease on the envelope. However, the user is inconvenienced, because he has to operate the manually-operable lever whenever it is necessary to print on the envelope.